• 想办法在程序启动的时候执行一次方法交换
• 方法1需要每个类都添加一个方法 然后调用
• 方法2将所有遵守协议SwizzleProtocol的类遍历 调用协议方法
  // 001

extension ViewController {
    static func yy_swizzle() {
        guard let m1 = class_getInstanceMethod(self, #selector(viewWillAppear(_:))) else {
            return
        }
        guard let m2 = class_getInstanceMethod(self, #selector(swizzle_viewWillAppear(_:))) else {
            return
        }
        
        if (class_addMethod(self, #selector(swizzle_viewWillAppear(_:)), method_getImplementation(m2), method_getTypeEncoding(m2))) {
            class_replaceMethod(self, #selector(swizzle_viewWillAppear(_:)), method_getImplementation(m1), method_getTypeEncoding(m1))
        } else {
            method_exchangeImplementations(m1, m2)
        }
    }
    
    @objc func swizzle_viewWillAppear(_ animated: Bool) {
        swizzle_viewWillAppear(animated)
        print("swizzle_viewWillAppear")
    }
}

/*
 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    ViewController.yy_swizzle()
 return true
 }
 */

// 002

extension ViewController: SwizzleProtocol {

    static func swizzle() {
        guard let m1 = class_getInstanceMethod(self, #selector(viewWillAppear(_:))) else {
            return
        }
        guard let m2 = class_getInstanceMethod(self, #selector(yy_viewWillAppear(_:))) else {
            return
        }
        
        if (class_addMethod(self, #selector(yy_viewWillAppear(_:)), method_getImplementation(m2), method_getTypeEncoding(m2))) {
            class_replaceMethod(self, #selector(yy_viewWillAppear(_:)), method_getImplementation(m1), method_getTypeEncoding(m1))
        } else {
                method_exchangeImplementations(m1, m2)
        }
    }
    
    @objc func yy_viewWillAppear(_ animated: Bool) {
        yy_viewWillAppear(animated)
        print("yy_viewWillAppear")
    }
}


protocol SwizzleProtocol {
    static func swizzle()
}

class Swizzle {
    // 获取到所有的类，遍历类，遵守协议AwakeProtocol的类执行awake方法
    static func performOnce() {
        let count = Int(objc_getClassList(nil, 0))
        let classes = UnsafeMutablePointer<AnyClass?>.allocate(capacity: count)
        let autoreleaseClasses = AutoreleasingUnsafeMutablePointer<AnyClass>(classes)
        objc_getClassList(autoreleaseClasses, Int32(count))
        for index in 0..<count {
            (classes[index] as? SwizzleProtocol.Type)?.swizzle()
        }
        classes.deallocate()
    }
}

/*
 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    Swizzle.performOnce()
    return true
 }
 */